The Ferrocene‐Based Complex Enables Defect‐Suppressed and Strain‐Relaxed Interfaces in Inverted Perovskite Solar Cells

ABSTRACT Inverted (p‐i‐n) perovskite solar cells offer advantages such as low fabrication temperatures and minimal hysteresis, but their performance is limited by energy level misalignment and non‐radiative recombination at the hole transport layer/perovskite interface. Poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA), a common hole transport material, has a hydrophobic surface and poor interface contact with perovskite, limiting device efficiency and stability. To address this, we introduce 1,1'‐bis(diphenylphosphino)ferrocene (DPPF), a traditional ferrocene‐based complex with dual phosphine coordination sites, for interface modification between PTAA and perovskite. DPPF optimizes energy level alignment, reduces the hole extraction barrier, and forms strong coordination bonds with uncoordinated Pb 2+ in the perovskite, passivating defects and suppressing carrier recombination. DPPF modification also improves perovskite film quality, enhancing crystallization, grain size, and reducing residual stress. The resulting inverted perovskite solar cell with a PTAA/DPPF hole transport layer achieves a power conversion efficiency of 24.3%, with a V oc of 1.133 V. The modified device shows excellent long‐term stability, retaining over 83% of initial efficiency after 1500 h of storage in ambient air. This work highlights DPPF's potential as an effective interface modifier for perovskite solar cells.